Download the following files:

Here is the step by step guideline to install Android N on Mi 3:

Step 1: Download all the files from above link and put the files into phone SD card storage (Not inside any folder)

Step 2: Now boot the device into TWRP recovery mode. To do this press volume down and power button at the same time.

Step 3: Perform a factory reset. To do this go to Wipe->Advanced Wipe->Select Wipe Cache, Dalvik System Cache, and data. Then Swipe to confirm the action.

Step 4: Return to recovery main menu window and click on “Install”. Now navigate to the downloaded ROM file and swipe to confirm the flashing process. Do the same flash process for both ZeurionX Kernel and GAAP.

Step 5: Wipe Cache and Dalvik Cache again from the recovery main menu again and reboot your device.